Voltage-nonlinear resistors

ABSTRACT

The invention relates to voltage-nonlinear resistors having nonohmic resistance due to the bulk thereof and more particularly to varistors, are suitable for use as elements of lightning arresters, comprising zinc oxide, bismuth oxide, antimony oxide and cerium fluoride.

[ 1 Sept. 24, 1974 United States Patent [1 1 Matsuoka et al.

VOLTAGE-NONLINEAR RESISTORS Inventors: Michio Matsuoka; Yoshikazu [58] Field 01lSearch.......... 338/13, 20, 21; 252/518;

Kobayashi; Gen Itakura; Takeshi Masuyama, all of Osaka, Japan References Cited UNITED STATES PATENTS 3,611,073 Hamamoto 3,632,528 1/1972 Matsuoka et al. 3,658,725 4/1972 Masuyama et al.... 3,778,743 12/1973 Matsuoka 22 Filed:

Primary Examiner-C. L. Albritton Application Pri rity Data Attorney, Agent, 0) FirmWenderoth, Lind & Ponack Japan 972 Japan......

Japan...

as elements of lightning arresters, comprising zinc ox- July 26,

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ide, bismuth oxide, antimony oxide and cerium fluoride.

S e r u .m F g .m w a r B 3 s m i m C 6 0 21 007 3 k 0 NH 3 3 U St Uh N1 1 VOLTAGE-NONLINEAR RESISTORS Various voltage-nonlinear resistors such as silicon carbide varistors, selenium rectifiers and germanium or silicon p-n junction diodes have been widely used for stabilization of voltage of electrical circuits or suppression of abnormally high surge induced in electrical circuits The electrical characteristics of such a nonlinear resistor are expressed by the relation:

I (V/C) (n where V is the voltage across the resistor, l is the current flowing through the resistor, C is a constant corresponding to the voltage at a given current and exponent n is a numerical value greater than 1. The value of n is calculated by the following equation:

gw(l2/l1)/l0gm( 2/ 1) (2) where V and V, are the voltages at given currents l and 1 respectively. The desired value of C depends upon the kind of application to which the resistor is to be put. lt is ordinarily desirable that the value of n be as large as possible since this exponent determines the extent to which the resistors depart from ohmic characteristics. Conveniently, the n-value defined by l l V, and V as shown in equation (2) is expressed by n to distinguish it from the n-value calculated by other currents or voltages.

Nonlinear resistors comprising sintered bodies of zinc oxide with or without additives and non-ohmic electrode applied thereto, have already been disclosed as seen in U.S. Pat. Nos. 3,496,512, 3,570,002 and 3,503,029. The nonlinearity of such varistors is attributed to the interface between the sintered body ofzinc oxide with or without additives and the silver paint electrode and is controlled mainly by changing the compositions of said sintered body and silver paint electrode. Therefore, it is not easy to control the C- value over a wide range after the sintered body is prepared. Similarly, in varistors comprising germanium or silicon p-n junction diodes, it is difficult to control the C -value over a wide range because the nonlinearity of these varistors is not attributed to the bulk but to the p-n junction. In addition, it is almost impossible for the varistors and germanium or silicon diode varistors to obtain the combination of C-value higher than I00 volts, n-value higher than 10 and high surge resistance tolerable for a surge of more than 100A.

On the other hand, the silicon carbide varistors have nonlinearity due to the contact between the individual grains of silicon carbide bonded together by a ceramic binding material, i.e., to the bulk, and the C-value is controlled by changing dimension in the direction in which the current flows through the varistors. In addition, the silicon carbide varistors have high surge resistance which is suitable for characteristic elements of lightning arresters. The characteristic elements are used usually by connecting in series with discharging gaps and determine the level of the discharging voltage and the follow current. The silicon carbide varistors, however, have a relatively low n-value ranging from 3 to 7 which results in poor suppression of lightning surge or increase in the follow current. Another defect of the arrester including the discharging gaps as its components is not to respond instantaneously surge voltage having very short rise time such as below lps. It is desirable for the arrester to suppress the lightning surge and the follow current to as low a level as possible and to respond to surge voltage instantaneously.

There have been known, on the other hand, voltagenonlinear resistors of bulk type comprising a sintered body of zinc oxide with additives comprising bismuth oxide and antimony oxide and/or chromium oxide, as seen in US. Pat. No. 3,663,458. These zinc oxide varistors of bulk type are controllable in a C-value by changing the distance between electrodes and have an excellent nonlinear property With an n-value more than 10 in a region of current below than l0A/cm For a current more than l0A/cm however, the n-value goes down to a value below than llt). The power dissipation for surge energy shows a relatively low value compared with that of the conventional silicon carbide arrester, so that the change rate of C-value exceeds 20 percent after two standard lightning surges of 4Xl0us wave form in a peak current of 1,500A/cm are applied to said zinc oxide varistor of the bulk type. There is known another zinc oxide varistor of bulk type which contains as an additive cerium fluoride as disclosed in the co-pending application Ser. No. 29416 filed in Apr. 17, l970. This varistor shows an excellent nonlinear property, but an essentially weak point as an arrester element is its weakness with respect to surge pulse. The nonlinear property of the varistor deteriorates easily even for l00A/cm of surge pulse.

An object of the present invention is to provide a voltage-nonlinear resistor having nonlinearity due to the bulk thereof and being characterized by a high n value even in a range of current more than l0A/cm Another object of the present invention is to provide a voltage-nonlinear resistor having high power dissipation for surge energy.

Another object of the present invention is to provide an arrester characterized by high suppression for lightning surge and low follow current.

These and other objects of the invention will become apparent upon consideration of the following description taken together with the accompanying drawing in which FIG. 1 is a partial cross-sectional view through a voltage-nonlinear resistor in accordance with the invention and FIG. 2 and FIG. 3 partial cross-sectional views through an arrester in accordance with the invention.

Before proceeding with a detailed description of the voltage-nonlinear resistors contemplated by the invention, their construction will be described with reference to FIG. 1 wherein reference character 10 designates, as a whole, a voltage-nonlinear resistor comprising, as its active element, a sintered body having a pair of electrodes 2 and 3 applied to opposite surfaces thereof. Said sintered body 1 is prepared in a manner hereinafter set forth. Wire leads 5 and 6 are attached conductively to the electrodes 2 and 3, respectively, by a connection means 4 such as solder or the like.

A voltage-nonlinear resistor according to the inven tion comprises a sintered body of a composition comprising, as an additive, 0.l to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimony oxide (Sb O and 0.1 to 3.0 mole percent of cerium fluoride (CeF and the remainder of zinc oxide (ZnO) as a main constituent, and electrodes applied to opposite surfaces of said sintered body. Such a voltagenonlinear resistor has non-ohmic resistance due to the bulk itself. Therefore, its C-value can be changed without impairing the n-value by changing the distance between said opposite surfaces. According to the invention, said resistor has high n-value in a region of current more than lOA/cm and high stability for surge pulses.

The higher n-value in a region of current more than lA/cm can be obtained when said sintered body further includes one member selected from the group consisting of0.l to 3.0 mole percent of cobalt oxide (C00) and 0.1 to 3.0 mole percent of manganese oxide (MnO).

According to the present invention, the higher nvalue in a region of current more than l0A/cm and the higher stability for surge pulses can be obtained when said sintered body comprises, as a main constituent, zinc oxide (ZnO) and, as an additive 0.1 to 3.0 mole percent of bismuth oxide (Bi O- 0.05 to 3.0 mole percent of antimony oxide (Sb O 0.1 to 3.0 mole percent of cerium fluoride (CeF 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganese oxide (MnO) and one member selected from the group consisting of 0.05 to 3.0 mole percent of chromium oxide (Cr O 0.1 to 3.0 mole percent of tin oxide (SnO and 0.1 to 10.0 mole percent of silicon dioxide (SiO According to the present invention, the resistor is remarkably improved in the n-value in a region of current more than l0A/cm and the stability for surge pulse when said sintered body consists essentially of 99.4 to 72 mole'percent of zinc oxide (ZnO) and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimony oxide (Sb O 0.1 to 3.0 mole percent of cerium fluoride (CEFg), 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.] to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr O and 0.] to 10.0 mole percent of silicon dioxide (SiO According to the present invention, when at least one voltage-nonlinear resistor consisting essentially of a sintered body of a composition comprising as a main constituent, zinc oxide and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimony oxide (Sb O and 0.1 to 3.0 mole percent of cerium fluoride (CeF and electrodes applied to opposite surfaces of said sintered body are applied to an arrester as a characteristic element, the resultant arrester is lowered in the follow current and improved in the suppression and power dissipation for lightning surges.

According to the present invention, when at least one voltage-nonlinear resistor consisting essentially of a sintered body of 99.4 to 72.0 mole percent of zinc oxide (ZnO), 0.1 to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimony oxide (Sb O 0.1 to 3.0 mole percent of cerium fluoride (CeF 0.1 to 3.0 mole percent of cobalt oxide (C00), 0.1 to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr O and 0.1 to 10.0 mole percent of silicon dioxide (SiO and electrodes applied to opposite surfaces of said sintered body are applied as a characteristic element to an arrester, the resultant arrester is further lowered in the follow current and is further improved in the suppression and power dissipation for lightning surges.

The sintered body 1 can be prepared by a per se well known ceramic technique. The starting materials in the compositions in the foregoing description are mixed in a wet mill so as to produce homogeneous mixtures. The mixtures are dried and pressed in a mold into desired shapes at a pressure from 50 I(g./cm to 500 Kg./cm The pressed bodies are sintered in air at l,00O to 1,450C for l to 10 hours, and then furnacecooled to room temperature (about 15C to about 30C). The mixtures can be preliminarily calcined at 700 to l,000C and pulverized for easy fabrication in the subsequent pressing step. The mixture to be pressed can be admixed with a suitable binder such as water, polyvinyl alcohol, etc. It is advantageous that the sintered body be lapped at the opposite surfaces by abrasive powder such as silicon carbide in a particle size of 50p. in mean diameter to 10a in mean diameter. The sintered bodies are provided, at the opposite surfaces thereof with electrodes in any available and suitable method such as silver painting, vacuum evaporation or flame spraying of a metal such as Al, Zn, Sn etc.

The voltage-nonlinear properties are not practically affected by the kinds of electrodes used, but are affected by the thickness of the sintered bodies. Particularly, the C-value varies in proportion to the thickness of the sintered bodies, while the n-value is almost independent of the thickness. This surely means that the voltage-nonlinear property is due to the bulk itself, but not to the electrodes.

Lead wires can be attached to the electrodes in a per se conventional manner by using conventional solder. It is convenient to employ a conductive adhesive comprising silver powder and resin in an organic solvent in order to connect the lead wires to the electrodes. Voltage-nonlinear resistors according to this invention have a high stability to temperature and for the surge test, which is carried out by applying lightning surge determined by the J EC (Japanese Electrotechnical Committee)-l56 Standard. The n-value and C-value do not change remarkably after heating cycles and surge test. It is advantageous for achievement of a high stability to humidity and high surges that the resultant voltagenonlinearresistors are embedded in a humidity proof resin such as epoxy resin and phenol resin in a per se well known manner.

When voltage-nonlinear resistors according to this invention are used as a characteristic element, the resultant arrester is improved remarkably in the follow current and the suppression property for lightning surge. FIG. 2 is the cross-sectional view of an arrester wherein reference character 20 designates, as a whole, an arrester comprising, one or more voltage-nonlinear resistors according to this invention 11 as a characteristic element are connected in series with one or more discharging gaps l2, spring 13 and line terminals 14 and 15. Said arrester elements are enveloped into wetprocess porcelain 16. Said arrester is kept to a level below luA in follow current and to a level higher than 2,000A/cm in surge dissipation. FIG. 3 is the crosssectional view of another arrester wherein reference character 30 designates, as a whole, an arrester comprising at least one voltage-nonlinear resistor according to this invention. In the embodiment shown in FIG. 3, reference characters identical to those of FIG. 2 have been employed to designate like elements. The arrester of FIG. 3 is characterized, in its construction, as without a discharging gap and, in its electrical properties, as having a time shorter than 0.1us for high surges having very sharp rise, in addition to its excellent properties, in follow current and surge dissipation. Presently preferred illustrative embodiments of the invention are as follows. Example 1 A starting material composed of 98.0 mole percent of zinc oxide, 0.5 mole percent of bismuth oxide, 1.0 mole percent of antimony oxide, and 0.5 mole percent of cerium fluoride is mixed in a wet mill for 24 hours. The mixture is dried and pressed in a mold into discs of 40mm in diameter and mm in thickness at a pressure of 250Kg/cm The pressed bodies are sintered in air at the condition shown in Table 1, and then furnace-cooled to room temperature. The sintered body is lapped at the opposite surfaces thereof into the thickness shown in Table 1 by silicon carbide abrasive in particle size of p. in mean diameter. The opposite surfaces of the sintered body are provided with a spray metallized film of aluminum in a per se well known technique.

The electric characteristics of resultant sintered body are shown in Table 1, which shows the C-value varies approximately in proportion to the thickness of the sintered body while the n-value is essentially independent of the thickness. It will be readily realized that the voltage-nonlinear property of the sintered body is attributed to the sintered body itself.

Zinc oxide incorporated with bismuth oxide, antimony oxide, and cerium fluoride in the composition of Table 2 is fabricated into the voltage-nonlinear resistors by the same process as that of Example 1. The thickness is 20mm. The resulting electrical properties are shown in Table 2, in which the values of n, and n are the n-values defined between 0. lmA and lmA, and

between 100 and l,OO0A, respectively. The impulse test is carried out by applying 2 impulses of 4 l0p.s, 10,000A. It can be easily understood that the combined addition of bismuth oxide, antimony oxide, and cerium fluoride as additives show the high n-value and small change rates.

Table 2 Additive (mol. Resultant Resistor Test C n n 131,0 s1 ,o CeF (at lmA) 0.l-lmA l00-l000A AC An, A",

0.1 0.05 0.1 1350 11 10 -17 -15 -s.0 0.1 0.05 3.0 1070 12 11 l6 -17 -7.7 0.1 3.0 0.1 1900 11 10 -16 -14 -7.6 0.1 3.0 3.0 1730 12 10 -16 -16 -7.1 3.0 0.05 0.1 2200 12 12 -15 -15 5.1 3.0 0.05 3.0 1940 13 11 -17 -14 -73 3.0 3.0 0.1 2430 12 10 -15 -13 -4.4 3.0 3.0 3.0 2200 11 11 -16 13 -46 0.5 1.0 0.5 l820 14 13 -13 -12 3.7

Table 1 EXAMPLE 3 Zinc oxide and additives of Table 3 are fabricated Thickness C Simcring into the voltage-nonlinear resistors by the same process (mm) (at lmA) 0.l-1mA Condition as that of Example 1. The electrical properties of the resulting resistors are shown in Table 3. The change initial 20 1820 14 1200c. SHrs rates of C and n values after the impulse test are carried 15 1345 14 1200ZC. SHrs out by same method as that of Example 2 and are also 10 910 13 1200 c. SHrs 5 455 14 1200c. 5Hrs shown in Table 3. It will be read1ly realized that the furinit 0) 1700 13 Wk theraddition of cobalt oxide or manganese oxide re- 15 1260 13 1350C. 1111 h I h I d n h t th 355 12 350C su s 1n a 1g er n-va ue an sma er c ange ra es an 5 430 12 1350C. 1H1 those of Example 2.

Table 3 Additive (mol. Electrical Properties of Change Rates after Test Resultant Resistor Bi O Sb O CeF- CoO MnO C n n AC An An (at 1111A) 0.1-lmA loo-1000A 0.1 0.05 0.1 0.1 950 17 12 -14 -14 8.2 0.1 0.05 0.1 3.0 1100 17 12 -14 -13 5.6 0.1 0.05 3.0 0.1 920 l8 12 -12 -12 -6.4 0.1 3.0 0.1 0.1 1300 18 12 -14 -13 6.2 3.0 0.05 0.1 0.1 1120 17 13 -13 -14 6.2 0.1 0.05 3.0 3.0 I080 l8 13 -12 -12 -5.7 0.1 3.0 0.1 3.0 1310 20 12 -13 -11 6.4 3.0 0.05 0.1 3.0 1290 21 13 -14 -12 -7.1 0.1 3.0 3.0 0.1 1230 20 13 -14 -12 -6.1 3.0 0.05. 3.0 0.1 1150 19 12 -13 -13 -5.4 3.0 3.0 0.1 0.1 1510 18 13 -13 -13 6.l 0.1 3.0 3.0 3.0 1500 20 12 -14 -10 -5.3 3.0 0.05 3.0 3.0 1470 19 11 -12 -10 -7.2

Electrical Properties of Change Rates after Additive (mol.

Sb O CeF 34265334543545434544 l l l l l l l l l l l l l l l l l l lll oos o o oo oo oos ooos o o oo oooos EXAMPLE 5 The resistors of Example 2, 3 and 4 are tested in acordance with a method widely used in the electronic components parts. The heating cycle test is carried out by repeating 5 times the cycle in which said resistors are kept at 85C ambient temperature for 30 minutes, cooled rapidly to C and then kept at such temperates. The humidity test is carried out at 40C and 95 percent relative humidity for 1,000 hrs. Table 5 shows the average change rates of C-value and n-value of resistors after heating cycle test and humidity test. It is easily understood that each sample has a 35 small change rate.

Table 4 Electrical Properties of Change Rates after Resultant Resistor Test C n z sio (at 0.1-lmA lOO-IOOOA AC An, An

lmA)

EXAMPLE4 Additives (mol.%)

ctr C00 MnO sno 0: 0;,

tai o Zinc oxide and additives of Table 4 are fabricated C into the voltage-nonlinear resistors by the same process as Example 1. The electrical characteristics of resulting resistors are shown in Table 4. It will be easily understood that the further addition of tin oxide, chromium oxide, silicon dioxide or chromium oxide and silicon m f 30 i dioxide results in the higher n-value and smaller change rates than those of Example 3. The change rates of C and n values after the impulse test are carried out by the same method as that of Example 2 are also shown in Table 4.

ISO-[50150 ll sssooo lll555000 lll555000 lll555000 .31s355 8787 778 :IT?

lll555000 ll sssooo lll333 Il s-D5000 till-355000 lll555000 lll555000 Table N H t'ng cycle Testj%) Humidity TesttS) Sample 0 A C 1 An, An AC An An;

Example 2 -48 6.2 5.0 5.2 6.7 6.1 Example 3 w 2.9 5.7 3.6 3.5 -5.2 -39 Example 4 l.8 -3.7 1.3 -13 38 l.4

EXAMPLE 6 The voltage-nonlinear resistors according to Example 2, 3 and 4 are employed in the arrester construction shown in FIG. 2 by series connection of 3 pieces of resistor and 1 discharging gap. The C-value of said total pieces of voltage-nonlinear resistor is about 7,000V. The impulse test are carried out by applying 2 impulses of 4Xl0us, 1,500A/cm superposed on AC 3000V. The follow current of the arrester shows a value lower than l tA as shown in Table 6 and the change rates of electrical properties after the test show same results as the impulse test of Example 2, 3 and 4.

EXAMPLE 7 The voltage-nonlinear resistors according to Examples 2, 3 and 4 are employed in the arrester construction shown in FIG. 3 by series connection of 3 pieces of resistor. The value of C at said total pieces of voltage-nonlinear resistor is about 7,000V. The impulse tests are carried out by the same method as that of Example 6. The follow current shows a value lower than luA as shown in Table 6 and the change rates of electrical properties after testing show the same results as that of the impulse test in Examples 2, 3 and 4. Another impulse test is carried out by applying an impulse having the value of 0.0lus in rise time. The rise time of current flowing through said arrester is lower than 0.05; .5.

What is claimed is:

1. A voltage-nonlinear resistor consisting essentially of a sintered body of a composition comprising as a main constituent, zinc oxide (ZnO) and, as an additive, 0.1 to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimony oxide (Sb O and 0.1 to 3.0 mole percent of cerium fluoride (CeF and electrodes applied to opposite surfaces of said sintered body.

2. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes one member selected from the group consisting of 0.1 to 3.0 mole percent of cobalt oxide (C00) and 0.1 to 3.0 mole percent of manganese oxide (MnO).

3. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes 0.1 to 3.0 mole percent of cobalt oxide (C00), 0.1 to 3.0 mole percent of manganese oxide (MnO) and one member selected from the group consisting of 0.05 to 3.0 mole percent of chromium oxide (Cr O 0.1 to 3.0 mole percent of tin oxide (SnO and 0.1 to 10.0 mole percent of silicon dioxide (SiO 4. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body consisting essentially of 99.4 to 72.0 mole percent of zinc oxide (ZnO) 0.1 to 3.0 mole percent of bismuth oxide (Bi O 0.05 to 3.0 mole percent of antimony oxide (Sb O 0.1 to 3.0 mole percent of cerium fluoride (CeF 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr O and 0.1 to 10.0 mole percent of silicon dioxide (SiO 5. An arrester comprising at least one voltagenonlinear resistor of claim 1 as a characteristic element.

6. An arrester comprising at least one voltagenonlinear resistor of claim 4 as a characteristic element. 

2. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes one member selected from the group consisting of 0.1 to 3.0 mole percent of cobalt oxide (CoO) and 0.1 to 3.0 mole percent of manganese oxide (MnO).
 3. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body further includes 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganese oxide (MnO) and one member selected from the group consisting of 0.05 to 3.0 mole percent of chromium oxide (Cr2O3), 0.1 to 3.0 mole percent of tin oxide (SnO2) and 0.1 to 10.0 mole percent of silicon dioxide (SiO2).
 4. A voltage-nonlinear resistor defined by claim 1, wherein said sintered body consisting essentially of 99.4 to 72.0 mole percent of zinc oxide (ZnO) 0.1 to 3.0 mole percent of bismuth oxide (Bi2O3), 0.05 to 3.0 mole percent of antimony oxide (Sb2O3), 0.1 to 3.0 mole percent of cerium fluoride (CeF3), 0.1 to 3.0 mole percent of cobalt oxide (CoO), 0.1 to 3.0 mole percent of manganese oxide (MnO), 0.05 to 3.0 mole percent of chromium oxide (Cr2O3) and 0.1 to 10.0 mole percent of silicon dioxide (SiO2).
 5. An arrester comprising at least one voltage-nonlinear resistor of claim 1 as a characteristic element.
 6. An arrester comprising at least one voltage-nonlinear resistor of claim 4 as a characteristic element. 